An existing universal gasoline engine fuel tank cover mainly comprises an outer shell, a card lock pedestal, a plastic disc, a card lock slice and a fuel tank inner cover. The outer shell and the card lock pedestal are riveted and a plastic disc is supported between the card lock pedestal and the outer shell, the plastic disc has a fuel tank inner cover disposed in the bottom cavity thereof, the card lock pedestal has a card lock slice connected to the bottom thereof, the plastic disc has a plurality of projected ribs disposed at the top portion thereof, the projected ribs being disposed with air gaps thereon, the plastic disc, fuel tank inner cover, card lock pedestal and card lock slice being respectively disposed with ventilation holes, and the fuel tank inner cavity being connected to the atmosphere through these ventilation holes when the fuel tank is covered. When the universal engine is running, air enters the fuel tank through the ventilation holes on the plastic disc, the fuel tank inner cover, the card lock pedestal and the card lock slice respectively to supplement the air pressure in the fuel tank so as to ensure regular supply of gasoline in the fuel tank to the engine. When the universal engine stops running, the gasoline vapor in the fuel tank is directly exhausted to the atmosphere through these ventilation holes. In addition, when the universal engine is excessively tilted or inclined, gasoline in the fuel tank will still flow out through this ventilation channel, and this does not only cause fuel wastage but also environmental pollution. In order to overcome the problems associated with direct exhaust of volatilized gasoline to the atmosphere and gasoline leakage during pouring, many manufacturers use carbon canisters and pour valves. However, as carbon canisters and pour valves are separate parts, assembly is made complicated and manufacturing cost is increased.